Cannot activate addon "Import Images as Planes"
Interesting, according to the traceback, your "io_import_images_as_planes.py" add-on file is corrupted. The line in question should be a comment not a procedure. This error alone can be easily fixed with putting one # character at beginning that line, like this.

Python 3.5.1 (v3.5.1:37a07cee5969, Dec 6 2015, 01:54:25)(MSC v.1900 64 bit)] on win32


to

#Python 3.5.1 (v3.5.1:37a07cee5969, Dec 6 2015, 01:54:25)(MSC v.1900 64 bit)] on win32


However it most likely has other corruptions. My guess you got your add-on from the wrong place, because it should start with the line of

# ##### BEGIN GPL LICENSE BLOCK #####


A possible solution:

Open the

C:\Users\user\AppData|Roaming\Blender Foundation\Blender\2.76\scripts\addons\io_import_images_as_planes.py


file with a text editor like notepad, delete everything.

Get the add-on from the github repository.
https://raw.githubusercontent.com/sambler/myblenderaddons/master/io_import_images_as_planes.py

Ctrl-a Ctrl-c to copy everything, and paste it in your notepad.

Than try to install it again.